Radio receiving apparatus



Oct. 19 1926. 1,603,494

E. s, PRIDHAM ET AL RADIO RECEIVING APPARATUS Filed NOV. 8, 1924 2 Sheets-Sheet l anuimnmmul *Ef/@+7 @ff fj@ Oct. 19 1926. 1,603,494

E. s. PRIDHAM ET Ar.

RADIO RECEIVING APPARATUS Filed Nov. 8. 1924 2 Sheets-Sheet 2 ma/Moni M'/ J9 @nl im lid Patented @ein lg, i926.

llgllu F l C E ltmm .AND PETER L. JENSEN, F OAKLAND, CALFDRNI, ASSIGNORS Uf@ THE MAGNAVQX COMPANY, 0F SAN FRANCISCO,

@E MEZHA.

CALIFORNIA, A CORPORATION RADIO RECEVING APPARATUS.

.application led November B, 1924 Serial Tulio. 748,567.

|flhis invention relates to radio receiving apparatus. Q

rllhe object of the invention 1s to facilitate tuning of a receiving set employing one or more stages of radio frequency amphiication, and wherein capacity or inductance of the amplifying circuits is requlred to be tuned to the antenna circuit. This necessitates manipulation of a plurality of tuning devices, and where there are two stages of amplication the operator is confronted with the problem of keeping all three c1r cuits in proper resonance throughout the wave length scale when endeavorlng to tune in on a designated station.

lin and by the present invention we provide a unit control for simultaneously tuning said circuits so that the time and effort required in tuning is materially lessened. lin other words, instead of providing three separate controls for tuning purposes, a single control is provided, which simultaneously actuates two or more tuning devices, keeping all of the diderent circuits to be tuned in resonance at all times.

'By way of illustrating one manner of carrying out our invention, reference 1s made to the accompanying drawings, 1n whichllig. l shows a plan view of a receiving set embodying our invention;

2 shows a front elevation of the same;

lig. 3 shows a vertical sectional view through the middle portion of the panel;

shows a diagram of the circuits employed in connection with the specific form of apparatus herein illustrated.

While our invention is not concerned with particular wiring diagram, it will assist in .an understanding of the invention to refer generally to Fig. t, wherein R1 and R2 indicate the radio-frequency amplifying tubes, D the detector tube, and A1 and A2 the audio-freqiuency amplifying tubes. V1, V2, and V3 designate the variometers used in the three tuning circuits. The variometers may he of any desired form, and in the presont apparatus we show them as consisting of dat coils with the stator upon a panel 11 .and a rotor l2 carried upon a shaft 13, which shafts are journalled upon said panel l1. 'lihe three shafts upon which the rotors of the three variometers are carried are connected together for joint rotation. There are a variety of ways of edecting such joint rotation, and the one herein described and illustrated is to be considered merely as a preferred form. Fixed upon each of the shafts 13 is a pinion llt. Meshing with the pinion 14 on the central shaft are two toothed racks l5, one rack being arranged at the top of said pinions and the other at thev bottom thereof, and the two racks en tending in opposite directions and meshing at their outer ends with the pinion on vthe adjacent shaft. These racks are supported at each end upon a roller 16, which main tains them in mesh with the adjacent pinion. Lost motion or back-lash of the racks is prevented by a small tortion spring 17 bound on each of the two outer shafts 13. One end of the spring is anchored to the shaft, and the other end to a post 18 adjacent the shaft. The two springs are wound in opposite directions and constantly exert a small tension, tending to turn the two out/er shafts in opposite directions, thus maintaining a constant tension or friction upon the two outer shafts which serves to take upon 'any lost motion or play that may occur in the gearing which connects the three shafts together.

The central shaft 13 is actuated by a lmob 19, carrying a pinion 20 meshing with a gear 21flxed on said central shaft. 'lhe central shaft is preferably` provided with a pointer 22 co-operating with a graduated dial on the front of the cabinet which houses the set.

Turning the knob 19 will impart motion to all of the three shafts simultaneously, and on account of the arrangement of the toothed racks the two outer shafts will be turned in a direction opposite to the central shaft. 'lhe purpose of this opposite rotation is to minimize magnetic coupling between the three variometers, such as would occur if all of the variometers had their rotors in parallel planes. lt'will be noted` that the stators of the three variomters are in parallel planes, and at zero position the three rotors will be parallel.

However, due to the fact that the rotor of the central variometer turns in one direction and the rotors of the two other variometers turn in the opposite direction, the three rotors do not occupy parallel positions at any points except Zero and 180. Therefore, the likelihood of mutual inductance arising at any point within the extreme limits of the wave length scale is effectually overcome.

IVe find that if the three tuning circuits are once placed in proper resonance, they will remain so throughout the wave length scale. Therefore, to bring these circuits into resonance, We provide a variable condenser 23 for each of the tuning circuits, by means of which the capacitance of the circuits may be adjusted. These condensers are preferably placed within the cabinet, and while adjustable, they are not intended to be manipulated by the operator. The adjustment is a fixed one, and is intended to be done by an expert at the factory or place of assembly, and once properly set, the circuits will remain in resonance and the operator has merely to concern himself with the manipulation of the variometers, in order to bring the instrument into tune with various wave lengths.

The unit control of a plurality of tuning devices can alsobe applied to receiving sets of the neutrodyne type. In such cases the three variable condensers for the major tuning operation are connected together for joint movement. For local reception no further adjustment of the circuits will be necessary, but for fine timing each circuit should be provided with an individually adjustable condenser -in addition to the unit control condensers, whereby the product of the inductance and net capacity may be made the same for each circuit. The individually adjustable condensers likewise permit circuits to be placed in resonance and compensate for variations in the capacity of different tubes.

What we claim as new and desire to secure by Letters Patent is:

l. In a radio receiving apparatus employing tuned radio frequency, a variometer for the antenna circuit and a variometer for each of the two radio frequency amplifying circuits, a panel on which said variometers are arranged, a pinion on the shaft of each rotor of said variometers, a pair of toothed racks meshing with the pinion on the rotor of the intermediate variometer, said racks extending in opposite directions and meshing with the pinions of the variometers at either side, in such manner as to cause opposite movement of the rotors at the side with respect to the rotor of the intermediate variometer.

2. In a radio receiving apparatus, a plrr rality of tuning circuits, a variometer in each circuit, each of said variometers including a rotor, a shaftfor each rotor journalled on a panel, a pinion on each shaft, a toothed rack connecting pinions of adjacent shafts together for joint rotation in opposite directions, and a tension spring on certain of said shafts, tending to turn them in opposite directions, whereby to take up slack in the connections.

EDWIN S. PRIDI-IAM. PETER L. JENSEN. 

